1. Field of the Invention
The present invention relates to diffusion bonds between components formed of two-phase metal alloy. More particularly, the present invention relates to a palladium-based aid material and a process for using the palladium-based material to form a diffusion bond between components formed of a tungsten heavy alloy.
2. Background Information
Large size and/or geometrically complex two-phase metal alloy materials, such as tungsten heavy alloy (WHA), are difficult to produce as a single piece. Accordingly, multiple two-phase metal alloy parts of uniform composition and properties can be joined to form a larger and/or a complex structure. However, problems in producing such parts arise from high machining costs to produce intricate shapes or limitations of the liquid phase sintered (LPS) consolidation process, such as maximum furnace size, severe slumping of parts, runout of liquid phase matrix material, and substantial compositional variation over the part height due alloying elements, such as solid tungsten particles in WHA, settling under gravity.
Materials, such as copper, have been previously used to join WHA materials. For example, U.S. Pat. No. 4,736,883 describes the joining of parts formed of WHA materials containing Ni, Fe, and/or Cu by diffusion bonding using a foil aid material of pure Cu or a Cu-based alloy. However, copper does not alloy with tungsten. This results in the rejection of tungsten from the parent material matrix in the bond region and the undesirable growth of large tungsten grains, and thus, an overall weaker bond between the parts formed of WHA materials. Similar difficulties can be encountered with other two-phase alloy materials.
Other joining processes and materials are known. For example, a solid-state diffusion bonding process is disclosed in U.S. Pat. No. 3,714,702; reactive brazing processes and brazing processes are disclosed in U.S. Pat. Nos., 3,276,113 and 5,704,538, and welding processes are disclosed in U.S. Pat. No. 3,110,101.
It would be desirable to improve the joining of thinner, smaller, and/or simpler components of WHA materials to form a monolithic structure with uniform properties.